D. Game
time limit per test
3 seconds
memory limit per test
256 megabytes
standard input
standard output

Allen and Bessie are playing a simple number game. They both know a function $$$f: \{0, 1\}^n \to \mathbb{R}$$$, i. e. the function takes $$$n$$$ binary arguments and returns a real value. At the start of the game, the variables $$$x_1, x_2, \dots, x_n$$$ are all set to $$$-1$$$. Each round, with equal probability, one of Allen or Bessie gets to make a move. A move consists of picking an $$$i$$$ such that $$$x_i = -1$$$ and either setting $$$x_i \to 0$$$ or $$$x_i \to 1$$$.

After $$$n$$$ rounds all variables are set, and the game value resolves to $$$f(x_1, x_2, \dots, x_n)$$$. Allen wants to maximize the game value, and Bessie wants to minimize it.

Your goal is to help Allen and Bessie find the expected game value! They will play $$$r+1$$$ times though, so between each game, exactly one value of $$$f$$$ changes. In other words, between rounds $$$i$$$ and $$$i+1$$$ for $$$1 \le i \le r$$$, $$$f(z_1, \dots, z_n) \to g_i$$$ for some $$$(z_1, \dots, z_n) \in \{0, 1\}^n$$$. You are to find the expected game value in the beginning and after each change.


The first line contains two integers $$$n$$$ and $$$r$$$ ($$$1 \le n \le 18$$$, $$$0 \le r \le 2^{18}$$$).

The next line contains $$$2^n$$$ integers $$$c_0, c_1, \dots, c_{2^n-1}$$$ ($$$0 \le c_i \le 10^9$$$), denoting the initial values of $$$f$$$. More specifically, $$$f(x_0, x_1, \dots, x_{n-1}) = c_x$$$, if $$$x = \overline{x_{n-1} \ldots x_0}$$$ in binary.

Each of the next $$$r$$$ lines contains two integers $$$z$$$ and $$$g$$$ ($$$0 \le z \le 2^n - 1$$$, $$$0 \le g \le 10^9$$$). If $$$z = \overline{z_{n-1} \dots z_0}$$$ in binary, then this means to set $$$f(z_0, \dots, z_{n-1}) \to g$$$.


Print $$$r+1$$$ lines, the $$$i$$$-th of which denotes the value of the game $$$f$$$ during the $$$i$$$-th round. Your answer must have absolute or relative error within $$$10^{-6}$$$.

Formally, let your answer be $$$a$$$, and the jury's answer be $$$b$$$. Your answer is considered correct if $$$\frac{|a - b|}{\max{(1, |b|)}} \le 10^{-6}$$$.

2 2
0 1 2 3
2 5
0 4
1 0
2 3
2 0
1 1 1 1

Consider the second test case. If Allen goes first, he will set $$$x_1 \to 1$$$, so the final value will be $$$3$$$. If Bessie goes first, then she will set $$$x_1 \to 0$$$ so the final value will be $$$2$$$. Thus the answer is $$$2.5$$$.

In the third test case, the game value will always be $$$1$$$ regardless of Allen and Bessie's play.